Prior art includes U.S. Pat. No. 3,432,881 disclosing gradually adjustable hinge members with means for releasing the operative angle of the hinge member fixed to the back rest relative to the seat hinge member. A similar adjustable two-part hinge fitting with a quick forward tilting release feature is disclosed in U.S. Pat. No. 3,432,880.
Additional prior art includes West German Patents Nos. 2,446,181 and 2,808,889 wherein a quick approximate ratchet and pawl adjustment within a limited range is combined with a gradual continuous taumel adjustment subject to interaction, however, preventing independent adjustment over the full range by either regardless of the position of the other.